In order to cover lateral surfaces and tops of buildings, coating elements in the form of modular panels are largely used, which should have high features of seal with respect to infiltrations, of thermal insulation and of mechanical resistance. That is why the structure of said panels typically consists of a layer of insulating material, for instance glass wool or polyurethane resin, enclosed in a metal envelope. The panel structure should further enable a good modularity, i.e. possibility of coupling more panels one with the other so as to obtain a continuous covering surface.
In the past it has been suggested to integrated a solar energy heating system for a fluid into a system for coating or covering buildings as referred to above.
In said light, document DE-A-28 16 970 describes panels for the external covering of buildings, comprising a core made of insulating material placed between an upper metal sheet and a lower metal sheet.
The panels described in the document mentioned above are rectangular and secured one beside the other on their respective long sides, the connection line between the panels being parallel with respect to the width of the surface of the building to be covered.
The upper metal sheet is covered by a further outer metal sheet, the two sheets being joined by welding, brazing or gluing; at least one of the two sheets has a series of ribs, so that the connection of said sheets results in a plurality of channels for a heat conveying fluid.
To this purpose, in particular there are provided for:                a series of first channels extending parallel one to the other and with respect to the long sides of the panel, and therefore parallel with respect to the width of the building surface to be covered,        two manifold channels, parallel one to the other and with respect to the short sides of the panel, therefore extending perpendicularly with respect to the first channels.        
The first channels communicate with the manifold channels, which are arranged each close to a respective short side of the panel. The end area of each manifold channel, on the upper surface of said channels, comprises holes for corresponding outer connections, connecting the manifold channels of a panel to the manifold channels of an adjacent panel, thus forming a system for the circulation of the heat conveying fluid.
The solution referred to in DE-A-28 16 970 is highly expensive as far as panel manufacturing is concerned, which envisages on one side the manufacturing of the upper portion of said panel through two metal sheets coupled one with the other, so as to form the various channels; in the embodiment described above, furthermore, a substantial part of the outer surface of the channels is not visible, i.e. it is not exposed directly to sun rays, which limits the possibility of heating the fluid by direct sun irradiation.
On the other side, also the installation of the covering system referred to in the prior document mentioned above is complex and expensive, since it envisages the use of a large number of panels and outer connections, the latter being also critical points as far as the hydraulic seal of the system is concerned; the same kind of fastening of the connections to the manifold channels, using screws and nuts, further complicates the mounting of the panels and their reciprocal hydraulic connections.
From document CH-A-619 770 it is also known a tile to be used for covering pitch roofs, having a single body made of metal, glass, cement conglomerate, terracotta or synthetic resin, having a flat portion and a curved portion placed side by side in longitudinal direction.
On top of the curved portion there is an outer groove, which can house and keep in position, through a respective pin, a length of dark-colored metal tube through which the fluid to be heated flows; the tile then has a glass cap covering, insulating and protecting said curved portion as well as the tube length supported by said portion. Thus, supposing that the groove is open upwards and the cap is transparent, the tube is exposed directly to sun rays.
The flat portion of the single body of the tile has hollow protuberances projecting upwards, having reflecting outer surfaces such that one of their areas is always placed in an optimal position with respect to sun rays, then reflecting the latter towards the tube whatever the position of the sun. Said protuberances are connected one to the other and to a cavity placed under the curved portion of the tile body, by means of ducts wherein air circulates, thus conveying heat absorbed in the area of the protuberances towards the cavity under the tube, so as to further heat the latter. The aforesaid ducts create in the upper portion of the tile reliefs preventing the longitudinal sliding of the glass cap.
For use, the tiles are nailed onto a heat insulating underground, which is secured in its turn onto a smooth plane resting on the roof load-bearing structure; it is thus possible to carry out a pitch roof, where the longitudinal tile rows house the aforesaid tubes, which extend therefore in a direction substantially perpendicular with respect to the width of the covered surface.
If the solution described in CH-A-619 770 on one side enables to obtain a roof with an aesthetical appearance substantially similar to the one of a common pitch tile roof, on the other it is complex and expensive as far as both tile manufacturing and tile installation are concerned, the latter envisaging also the installation of an underlying heat insulating system; the system described above, which is not suitable for covering vertical walls, further does not enable to obtain a roof structure with substantially monolithic panels, as is the case of DE-A-28 16 970, which is preferable in some applications (such as for instance the covering of industrial, commercial and similar buildings).